| Specifications | ATtiny202 | ATtiny402 |
|---|---|---|
| Flash (program memory) | 2048 bytes | 4096 bytes |
| Flash w/Optiboot | 1536 bytes | 3584 bytes |
| RAM | 128 bytes | 256 bytes |
| EEPROM | 64 bytes | 128 bytes |
| Bootloader | Optiboot (optional, not recommended) | Optiboot (optional, not recommended) |
| GPIO Pins | 6 (5 usable) | 6 (5 usable) |
| ADC Channels | 6 (5 usable) | 6 (5 usable) |
| DAC | No | No |
| PWM Channels | 4 | 4 |
| Timer Type B | 1 | 1 |
| Timer Type D | No | No |
| Interfaces | UART, SPI, I2C | UART, SPI, I2C |
| Clock options | Internal 20/16/10/8/5/4/1 MHz | Internal 20/16/10/8/5/4/1 MHz |
This matches the megaTinyCore 412/402 Rev. - and Rev. A breakout boards below. In 2.0.0 and later, this is no longer the case! You must call Serial.swap(1) prior to Serial.begin() to move it to the alt pins (or connect your adapter to pins 0 and 1 instead of 2 and 3). It should never have been done that way in the first place. A Rev. B of the breakout boards that has the FTDI header tied to the standard serial pins is planned for availability in May 2020.
There exist ATtiny402's in the wild where the last byte of the signature is 0x25, instead of 0x27. Currently shipping parts from Atmel/Microchip have the correct signature, and this problem appears to be in the past, for the most part. Hoerver, if you're stuck with wrong-signature ATtiny402's, choose ATtiny402 (bad signature) from the tools -> chip menu.